A. homing pigeons navigate by geomagnetic field and can fly home from thousands of miles away.
B. Mucus on loach can reduce friction and make it easy to escape.
C camel's feet are very wide, which can reduce the pressure on the ground and facilitate walking in the desert.
D In hot weather, dogs often stick out their tongues and use evaporation to absorb heat and cool down.
Solution: A, homing pigeons can identify the strength of the geomagnetic field and fly home from thousands of miles away.
B, loach mucus is under the condition of constant pressure, reduce the roughness of the contact surface to reduce friction.
C. The width of camel's feet means that under the condition of constant pressure, the stress area increases, reducing the pressure on the ground and facilitating walking in the desert.
D, there is water on the dog's tongue, which absorbs heat when it evaporates, thus achieving the effect of cooling down.
So choose C.
2.(20 12? Qinzhou) As shown in the figure, containers A and B are filled with the same quality of liquid. The pressure distribution of the liquid at the bottom of the two containers is F A and F B, and the pressure is P A and P B respectively, so their size relationship is (a).
Solution: (1)∵ Containers A and B are regular cylinders.
∴ The pressure difference of the liquid at the bottom of the two containers is F A =ρgh A× S A =ρgV A =m A G.
F B =ρgh B× S B =ρgV B =m B G
The two containers A and B contain the same liquid with the same mass.
∴ The bottoms of both containers are under the pressure of liquid, F A =F B,
(2)∫ha < H B，P=ρgh，
∴P A < p B，
So choose a.
An elevator apartment building is about 40 meters high. To complete the building, it is necessary to pour reinforced concrete 1× 104m3 and use other building materials. 3.5× 104t, and the concrete density is 2.5× 103kg/m3 (g is 10N/kg).
(1) It is known that the density of tap water is 1× 103kg/m3. How much pressure does the pressurizing equipment exert on the water supply to provide tap water from the underground to the roof?
(2) The measurement shows that the pressure on the building foundation should not exceed 1.2× 106Pa. If the contact area between the foundation and the ground is 1× 103m2, the total mass of additional decorative materials, various equipment and other substances and personnel entering the building shall not exceed.
answer
(1) The pressure P exerted by the pressurizing equipment on at least water is at least equal to the pressure generated by a 40m high water column. ∴ P at least = rho water GH =/kloc-0 /×103kg/m3×10n/kg× 40m = 4×105pa.
(2) The maximum bearing pressure of building foundation F max = P max s =1.2×1×1×103m2 =1.2×109N reinforced concrete weight G mix = Kloc-0/08N Other building materials weight G Other = M Other G = 3.5× From the topic: F max = G Mixed +G Other +M Total G ∴1.2×109n = 2.5×108n+3.
Xiao Ming experimented with a bottle full of pure water and a sponge on a horizontal table to explore "the factors affecting the stress effect". As shown in the figure, he found from the trademark that the "net content" of this bottle of water is 630ml (1ml =1cm3 =10-6m3); The bottom area of the bottle is 35cm2 and the cap area is 7cm2, ignoring the gravity of the empty bottle. According to the data collected by Xiao Ming, please calculate:
(1) What is the net weight of this bottle of pure water?
(2) What is the pressure on the sponge when the bottle is placed upright?
(3) What is the simplest way to make the pressure on the sponge be the same when the bottle is inverted?
answer
1) The mass of this bottle of purified water is: m = ρ V =1.0×103× 630×10-6 kg = 6.3n, so the weight of this bottle of purified water is g = mg = 0.63×1.
(2) The pressure of the bottle on the sponge is: p = f/s = g/s = 6.3/35×10-4pa =1.8×103pa.
(3) P 1=P2, that is, g/s1= g/S2, G/=GS2/S 1=G/5, that is, only 1/5 water can be left in the inverted bottle, so 4/5 can be poured out of the bottle.
5. In an ice-breaking operation, when the ship rushed to the ice surface, the displacement of the ship became one third of the original, and the contact area between the ship and the ice surface was 5m2. What is the pressure of the icebreaker on the ice at this time? (The density of seawater is 1.0× 103/m3).
answer
(1)F float = ρ water gV platoon =103x1.5xx103n =1.5xx107n because the ship floats.
(2)F float = 1/3ρ water gV discharge (1 min) P=F/S=2G/3S=2× 106Pa A person's mass is 6 1.8kg and density is1.
6. As shown in the figure, Xiaohua, a student with a mass of 48kg, rides a bicycle at a uniform speed of 500m on a straight highway, and the time it takes is 100s. Assume that the resistance of the bicycle when driving is112 of its weight.
Q: (1) The power that this classmate did during this period;
(2) If the mass of the bicycle is 12kg and the total contact area between the tire and the ground is 40cm2, what is the pressure of the bicycle on the ground when the classmate rides?
The answer (1) 200 w (2)1.5×10 to the fifth power.
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